Resistance-supporting structure



Patented Feb. 4, 1939 UNITED STATES PATENT OFFICE FERNALD S. STIGKNEY, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR T0 WESTING- HOUSE ELECTRIC & MANUFACTURENG COMPAKY, A. COEPORATION OF .PENNSYL- VANIA RESISTANCE-SUPEOETING STRUCTURE Application filed October 20, 1927. Serial No. 227,430.

My invention relates to a resistor supporting structure and has particular relation to an arrangement for supporting a plurality of resistor units.

In accordance with my invention, a plurality of resistor units are mounted in superposed relation on a base -or member formed, usually, of insulating material.

Further, in accordance with my invention,

the aforesaid resistor units are directly supported by a rod or stem, preferably of insulating material, which projects from said base or member.

Further, in accordance with my invention, the aforesaid resistor units are enclosed by a housing, perforated or otherwise, and preferably detachably related to the aforesaid base or member.

Further, in accordance with my invention, the various parts of my device are so proportioned and arranged that the creepage distance between energized sections is sufficient to prevent flashovers under normal operating conditions.

My invention resides in the structure, arrangement and features of construction of the character hereinafter described and claimed.

For an understanding of my invention and for an illustration of one of the forms my apparatus may take, reference is to be had to the accompanying drawing in which:

Figure 1 is a side elevational view of a structure constructed in accordance with my invention Fig. 2 is a vertical sectional view taken on the line 11-11 of Fig. 1;

Fig. 3 is a bottom plan view of the structure shown in Figs. 1 and 2;

Fig, 4 is a side elevational view, partly in section, of a plurality of resistor units.

Referring to the drawing, B is a base or supporting member of suitable insulating material and preferably molded from a phe nolic condensation product, or the like, as, for example, that known to the trade as moldarta. Member B comprises a wall or ledge 1 from which a circular rim or flange 2 extends or projects. As viewed in Fig. 2, the upper surface of wall 1 is substantially horizontal, with the exception of a centrallydisposed section 1a which extends upward y into the space encompassed by the wall 2 and terminates in a substantially flat, horizontal surface. The lower surface of the wall 1 is, preferably, substantially arcuate, as indicated by the broken line 1?), Fig. 1.

The exterior surfaces 3 and 3a of opposite side walls of the member B are flat and extend substantially in a vertical direction (Fig. 2). The lower portions of the side walls are cut away, substantially as indicated at 4; (Figs. 1 and 2), for a purpose hereinafter set forth. At the front and rear, the member B comprises arcuate outer surfaces 5 and 5a (Fig. 1), which extend substantially vertically above the respective horizontal fiat surfaces 6 and 6a, each of which is provided with a passage 7.

The section 1a and wall 1, centrally of the wall 2, are provided with a threaded passage into which is threaded one end of a rod or stem 8 formed, preferably, of insulating material, as hard rubber, a phenolic condensation product, or, and preferably, fibre. The rod 8 projects a suitable distance beyond the wall 1 and extends through and supports one or more resistor units or spools 9, adjacent pairs of which are separated by one or more sheets 10 of suitable insulating material. The resistor units or spools 9 are of a type well known to the art and, as illustrated in Fig. 4, are usually formed by winding a relatively small insulated wire to produce layers 11, adjacent layers being separated by a suitable insulating sheet 12.

The aforesaid side walls individually support a binding post or terminal of suitable character. In the example shown, each side wall is provided with an opening or perforation through which project conductive members or bolts 13 and 18a. The heads of members 13 and 1360 are disposed within the charm ber formed interiorly of member B below the surface 16, and between the-heads of members 13 and 18a and the interior surface of the adjacent side wall the respective ends of conductors 14k and 14a are disposed. Nuts 15 and 15a, threaded to the respective members 13 and 13a, maintain the headed ends of the latter in engagement with the ends of the respective conductors 14 and 14a. To

prevent casual disengagement of the nuts 15 and 15a, it is desirable that locking Washers 16 and 16a be associated therewith. Threaded to the respective ends of members 13 andlSa are the nuts 17 :and 17a by which conductors (not shown) of an electricalcircuit may be conductively related to the conductors 14 and 1400.

' Thewall 1 is provided with perforations through which the conductors 1 4 and 14 1!. project and, in the example'sh'own, conductor 14 is connected to one terminal of the lowermost resistance unit 9 (Fig. 2), all of which units are connected in any suitable circuit relation, for example, inseries, in whichcase, the conductor 14a is connected tothe otherwise free terminal ofthe highest unit 9, (Fig.2).

Ordinarily, it is desirable that the respective conductors 14 and 14a shall be disposed interiorly of'suitable insulating ;sleeves 18 and 18a which, preferably, are tube-like members formed from varnished cloth.

Fitting interiorly of the circular wall 2and usually engaging the upper surface of wall 1, is a housing structure 19 for the resistor units .9. Preferably, member 19 comprises a metallic tube,-on the upper end of which is disposed a cap .orcover20, (Fig.2), the tube being perforated for the liberation-of heat generated by the units 9. Ordinarily, as illustrated in Fig. 2, the upper end of rod 8 is threaded to receive a nut 21 by means of which movementof the units 9- with respect toeach other and the rod 8 is prevented. Furthermore, the extreme upper threaded end of rod 8 ordinarily projectsthrough the cap 20 to receive a nut 21 by which said cap is retained on the structure 19.

As illustrated in Fig. 2, it is desirable that a sheet 22 of suitable insulating material be confined within the cap 20 at the end of the tube-like member 19. r

A device of the character described above is utilizable as a resistor unit or element in any case where it is desirable or necessary to alter the resistance characteristics of anelec- --trical circuit. For example, the device is designed particularly for use as an external multiplier forfavoltmeter and, when so used, is connected in series with the energizing w-indingof :the voltmeter.

In the electricalarhtho term creepagedis tance isideiined'as theshontest distance along a surface between energized pants of anelectrical circuit at different potential. In accordance withmy invention, the proportions of the aforesaid deviceare so chosen that the creepage distances are ample to prevent has-hovers-under such voltage conditions as arerord'inarlly .met'ln PE-2105168.

When the -'housing structure 19 is of metal- "l-ie material, as it usually is, it :might occur, due to some abnormal condition, that said structure would become charged tosome potential, for example, that of the side of the circuit connected to the terminal 13, and this potential probably would differ greatly from the potential of the upper resistor unit 9, and particularly the upper portion thereof. Therefore, the creepagedistance along the rod 8, bet-ween the nut 21 and the cover 20 of the structure 19, is of amagnitude suificient to prevent a flashoverjunder normal ing conditions. Moreoverfthe j insulating sheet 21 functions to prevent a flashover between the parts mentioned above.

The conductors l4 and 14a and the lower surface of the lowest resistance unit 9 may be at different potentials. Therefore, the creep- .age distance between either conductor and said unit 9 is increased by the utilization of the pedestal or section 1a and-the insulating tubing 18 and 18a. Furthermore, the pedestal 1a increases the creepagedistance between .said unit 9 and the housing '19.

As stated above, the housing structure 19 might become charged to some potential differing from that of the terminals 13 and 13a and, hence, there would be liability of flashovers between one or both of said terminals and said housing structure. The provision of [the rim 2, however, increases the c-reepage distances betweenthe aforesaid parts and impedes or prevents the flashover danger.

Between the ends of conductors l4 and 14a coacting respectively, with the headed ends of terminals 13 and 13a, there is a long creepage distance along the lower surface of wall 1, (Fig. 2).

When utilized as a multiplier fora voltmeter, thedevice may bemountedon a metallic panel, which is usually at ground potential. F or thus securing-the base 13 to said panel, metallic screwszor bolts may be utilized to project through the passages 7 The provision of the rim 2, as aforesaid, increases the creepage distance ibetween said screws or bolts and the housing structure 19, (Fig. 1).

then the device is mounted on a metallic panel, as aforesaid, there is danger of flashover between the'sa'me andlone or both of the terminals 13 and 13a. Theprovision .of the cut-away portions 4 decreases this liability.

because providing creepage distances of re1atively great and SLlffiGleIlt length.

Each of the units 9 mayhavea resistance of any desired magnitude which may range upwardly to 50,000 ohms, or more. By propergselection ofth-e units 9, therefore, the total resistance of the. device may be chosen, avithinlimits. This mode of'resistanceiselecltion, however, may not be sufficiently accurate, at times, in which case, was illustrated particularly in Fig. 4, the upperwresistance 1 unit 9 may comprise .a spool on which" is wound a conductor, one .end :thereof ibeing connected to a -terminali24 at 125 :andsthenther end to a terminal 126 at 27. 'Ellhe connection operat- 27 may readily be detached, a certain amount of the resistance wire eliminated, and the connections reestablished. An adjustment of this character may readily be performed with a device of the character herein illustrated, since it is necessary only to remove the nut 21 and cover 20 to detach the structure 19 from base B.

The rod 8 and housing structure 19 may be of any desired or suitable length to accommodate, on said rod 8, any suitable number of the resistance spools 9.

A device of the character herein described is simple, comprises but few parts, is readily assembled, and constitutes a distinct advance in the art.

I claim as my invention:

1. An external resistor for an electrical instrument comprising a base of insulating material, electric terminals secured to a side wall of said base, said base having a cup-shaped recess in the upper face thereof, an electric resistor supported upon said base and electrically connected to said terminals, and a perforatedcasing surrounding said resistor and seated within said cup-shaped recess whereby a relatively long creepage distance between said terminals and said casing is provided.

2. An external resistor for an electrical instrument comprising a base of insulating material, said base comprising a substantially right-angled hollow cylinder having a substantially discoidal partition between the open ends of said cylinder, a threaded stud mounted on, and extending normal to, said partition, a plurality of electric terminals extending through, and secured to, opposite sides of the cylindrical portion of said base, said terminals and said stud being separated by said partition, a plurality of resistor coils of predetermined resistance mounted on said stud, the number of said resistor coils being variable at will to change their total resistance, relatively stiff insulated conductors secured to said terminals and extending through said partition for electrical connection to said resistor coils, said partition cooperating with said terminals to hold said conductors in position, and a perforated casing for said resistor coils removably secured to said base by means of said stud.

In testimony whereof, I have hereunto subscribed my name this 15th day of October 1927.

FERNALD S. STICKNEY. 

